Perceptual similarity models readily explain basic-level categorization. These models propose that, within a category, responses learned to one exemplar transfer to others through primary stimulus generalization. The inadequacy of perceptual similarity as the basis of all truly "conceptual" behavior is noted. Superordinate conceptual categories, for example, often combine basic-level categories encompassing exemplars which are perceptually very different from one another. The proposed studies examine mediated generalization and association as mechanisms of such superordinate categorization. The experiments in the present proposal use a three-step procedure to examine nonsimilarity-based categorization. In a paradigmatic study, diverse exemplars from two basic-level categories (C1 and C2) were associated with one common response (R1) and diverse exemplars from two other basic-level categories (C3 and C4) were associated with another response (R2) in original training. In reassignment training, exemplars from C1 and C3 were associated with new responses (R3 and R4, respectively) and exemplars from C2 and C4 were withheld. In a final test phase, performance of R3 vs. R4 was measured to the exemplars from C1, C2, C3, and C4. If the C1/C2 and C3/C4 combinations were bound into superordinate categories in the first step of training, then subjects should predominately make R3 to the C2 exemplars and R4 to the C4 exemplars. This result was obtained. The proposed studies will examine empirical and theoretical issues concerning mediated generalization and association in superordinate categorization using the three-step procedure. Superordinate conceptual categories are open sets. The word "furniture," for example, is not reserved solely for the familiar lamps and chairs of our own homes, but it is also applied to lamps and chairs we see for the first time. Experiments 1 and 2 of this proposal examine whether superordinate categories created by the three-step procedure are also open sets. Transfer tests with novel exemplars drawn from the component basic-level categories are added to the basic research design. If obtained, transfer of original training to novel exemplars and transfer from novel exemplars to the original training sets will demonstrate that the superordinate categories created in original training of the three-step procedure are indeed, open sets. Another issue to be addressed (in Experiments 3 through 7) concerns the types of training which might bind disparate basic-level categories into one superordinate category. Among the alternatives to be examined are association with: a common delay to reinforcement, reinforcement schedule, contextual stimulus, spatial location, and temporal contiguity. The empirical base established by these studies will give greater perspective on the theories to be considered in of the role of mediation in the formation of superordinate conceptual categories.